The idea behind this prophecy is that at some point Satan and/or his minions (both men and demons) will try to create either a fake rapture, a false messiah, an alien invasion, or any combination of the three, to trick the world into believing his lie, and to also discourage and potentially destroy the faith of the true believing church. Some believe that this event may come, not in the form of a mysterious "snatching away" of certain people, but rather as an alien invasion of sorts where demons (disguised as aliens) will come down to Earth to "rescue" the worthy. It's possible that even Lucifer himself may appear as a false Christ prior to the arrival of the man of sin. Note, this will not be THE AntiChrist, but rather just another false Christ.

The purpose of this alien deception will be to many away from Christ, and even possibly gather up many of those who will fall for this deception with the intent of slaughtering them. There are others (not those listed in the listed prophetical sources) who believe that this will instead be done by men under demonic control who will be directed to come against big name pastors and spiritual leaders with the help of something called "project blue beam" which is believed to have the capabilities of projecting large and very realistic holographic displays in the sky. Regardless of which way this unfolds, the idea that a fake rapture or false second coming is being planned, and that it will be used to deceive the whole world, is universally agreed upon. Only the means by which it will be done are up for debate as there seems to be no clear answer on that subject.

UPDATE (2018-02-02): I'm marking this one as "in progress" again as recently developments seem to be putting this prophecy in motion again.